Method of processing a semiconductor wafer

ABSTRACT

A method of processing a semiconductor wafer that has circuits in each of a plurality of regions sectioned by a plurality of streets on the front surface and has a coating layer formed on the front surface having the circuits to a predetermined thickness, the method comprising a stress-reducing step of reducing the stress of the coating layer by forming a plurality of grooves in the coating layer formed on the front surface of the semiconductor wafer; and a grinding step of processing the back surface of the semiconductor wafer by grinding to a predetermined thickness after the stress-reducing step.

TECHNICAL FIELD

[0001] The present invention relates to a method of processing asemiconductor wafer having a large number of circuits on the frontsurface to a predetermined thickness.

BACKGROUND ART

[0002] In the process of semiconductor device production, semiconductorchips are produced by forming a circuit such as IC, LSI or the like in aplurality of regions sectioned by a plurality of streets on the frontsurface of a substantially disk-like semiconductor wafer and dicingalong the streets. In order to improve the heat radiation of the thusmanufactured semiconductor chip, it is desired that the semiconductorchip be made as thin as possible. Also, to enable the downsizing of aportable telephone, smart card or personal computer that uses a largenumber of semiconductor chips, it is desired that the semiconductor chipbe made as thin as possible. To this end, before the semiconductor waferis divided into individual semiconductor chips by dicing, the backsurface of the semiconductor wafer is processed to a thickness of about50 μm by grinding.

[0003] When the back surface of the semiconductor wafer is ground toreduce its thickness, both sides of the semiconductor wafer are warpedtoward the front surface side. For example, when the back surface of asemiconductor wafer having a diameter of 200 mm is ground to a thicknessof 50 μm, both sides of the semiconductor wafer are warped toward thefront surface side by about 60 mm. It has been found that this warpingof the semiconductor wafer is caused by a coating layer formed byapplying a polyimide resin having excellent heat resistance, electricinsulating properties and mechanical strength to the front surface ofthe semiconductor wafer and baking it in order to protect circuitsformed on the front surface of the semiconductor wafer, or anothercoating layer such as a metal layer, insulating layer or the like. Thatis, a stress for pulling toward the center direction is generated in thecoating layer formed on the front surface of the semiconductor wafer.Therefore, when the back surface of the semiconductor wafer is processedto a thinness of about 50 μm thick by grinding, the semiconductor waferis warped as described above because its stiffness does not withstandthe above stress. When the semiconductor wafer is thus warped, it isdifficult to smoothly carry out dicing which is a subsequent step.

[0004] It is a principal technical subject of the present invention thathas been made in view of the above fact to provide a method ofprocessing a semiconductor wafer, which can inhibit the semiconductorwafer from being warped even when its back surface is ground to beprocessed thin.

DISCLOSURE OF THE INVENTION

[0005] To attain the above principal technical subject of the presentinvention, according to the present invention, there is provided amethod of processing a semiconductor wafer that has circuits in aplurality of regions sectioned by a plurality of streets on the frontsurface and has a coating layer formed on the front surface having thecircuits to a predetermined thickness, the method comprising:

[0006] a stress-reducing step of reducing the stress of the coatinglayer by forming a plurality of grooves in the coating layer formed onthe front surface of the semiconductor wafer; and

[0007] a grinding step of processing the back surface of thesemiconductor wafer by grinding to a predetermined thickness after thestress-reducing step.

[0008] The plural grooves to be formed in the coating layer in the abovestress-reducing step are formed along a plurality of streets.

[0009] The plural grooves to be formed in the coating layer in the abovestress-reducing step are formed by cutting by moving the semiconductorwafer relatively to the cutting blade while the cutting blade isrotated.

BRIEF DESCRIPTION OF THE INVENTION

[0010] FIGS. 1(a) and (b) are explanatory diagrams showing asemiconductor wafer to be processed according to the present invention;

[0011] FIGS. 2(a) and (b) are explanatory diagrams showing thestress-reducing step of the processing method of the present invention;

[0012] FIGS. 3(a) and (b) are explanatory diagrams showing the step ofaffixing a protective tape to the front surface of a semiconductor waferafter the stress-reducing step shown in FIGS. 2(a) and (b); and

[0013]FIG. 4 is an explanatory diagram showing the cutting step of theprocessing method of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0014] The method of processing a semiconductor wafer according to anembodiment of the present invention will be described in detailhereinafter with reference to the accompanying drawings.

[0015] FIGS. 1(a) and (b) show a semiconductor wafer to be processedaccording to the present invention. FIG. 1(a) is a perspective view ofthe semiconductor wafer and FIG. 1(b) is a partially enlarged sectionalview of the semiconductor wafer. The semiconductor wafer 2 shown inFIGS. 1(a) and (b) has a diameter of 200 mm and a thickness of 500 μm,and a circuit 22 is formed in each of a plurality of regions sectionedby a plurality of streets 21 on the front surface of the semiconductorwafer 2. A coating layer 23 as a protective film is formed on the frontsurface having the circuits 22. In the illustrated embodiment, thecoating layer 23 is formed by applying a polyimide resin to the frontsurface of the semiconductor wafer 2 including the circuits 22 andbaking it, and has a thickness of about 10 μm.

[0016] The back surface of the above-described semiconductor wafer 2 isground to process it to a thickness of about 50 μm before it is dividedinto individual semiconductor chips by dicing along the plurality ofstreets 21. When the semiconductor wafer 2 is processed thin, it iswarped by the influence of stress generated in the coating layer 23 asdescribed above. In the present invention, therefore, to inhibit theoccurrence of the above warping, the step of reducing stress that hasgenerated in the above coating layer 23, for pulling toward the centerdirection is carried out before the back surface of the semiconductorwafer 2 is ground.

[0017] FIGS. 2(a) and (b) show the stress-reducing step of reducing thestress of the coating layer 23. FIG. 2(a) is a perspective view of thestep and FIG. 2(b) is a partially enlarged sectional view of thesemiconductor wafer 2. In the stress-reducing step, as shown in FIGS.2(a) and (b), grooves 231 are formed in the coating layer formed on thefront surface of the semiconductor wafer 2. A cutting machine that isgenerally used as a dicing machine can be used for forming the grooves231. That is, the grooves 231 are formed in the coating layer 23 byholding the semiconductor wafer 2 on a chuck table 31 of the cuttingmachine and cut-feeding the chuck table 31 in a direction shown by anarrow X while a cutting blade 32 is rotated. It is desired that thegrooves 231 be formed along the streets 21 in order not to damage thecircuits 22. The depth of the grooves 231 is equivalent to the thicknessof the coating layer 23 so that the coating layer 23 is desirably cut.The grooves 231 do not need to be always formed along all the streets,and are enough to be formed to such an extent that the stress of thecoating layer 23 can be reduced and warping which occurs when thesemiconductor wafer 2 is made as thin as about 50 μm can be suppressed.For example, four grooves 231 may be formed per each direction, thoughthe grooves 231 may be formed along all the streets. As to cuttingconditions for forming the grooves 231, it is appropriate that therevolution speed of the cutting blade 32 is about 20,000 rpm and thefeed speed of the chuck table 31 is about 50 to 100 mm/sec.

[0018] After the stress-reducing step terminates, the semiconductorwafer 2 is turned upside down as shown in FIG. 3(a), and a protectivesheet 4 for grinding is affixed on the front side (on the circuit22-formed side), as shown in FIG. 3(b).

[0019] The grinding step for processing the back surface of thesemiconductor wafer 2 having the protective sheet 4 affixed on the frontsurface as described above to a predetermined thickness is then carriedout. That is, as shown in FIG. 4, the semiconductor wafer 2 is held onthe chuck table 51 of the grinding machine 5 in such a manner that theback surface faces up, and a grinding wheel 52 is rotated at arevolution speed of 6,000 rpm while the chuck table 51 is rotated at arevolution speed of 300 rpm, and is brought into contact with the backsurface of the semiconductor wafer 2 to grind the back surface of thesemiconductor wafer 2. The semiconductor wafer 2 is ground until itsthickness becomes about 50 μm. Even when the back surface of thesemiconductor wafer 2 is ground until its thickness becomes about 50 μm,the occurrence of warping is inhibited because the stress of the coatinglayer 23 has been reduced by forming a plurality of grooves 231 in thecoating layer 23 formed on the front surface of the semiconductor wafer2 in the above stress-reducing step.

[0020] The semiconductor wafer 2 whose back surface has been processedto a thickness of about 50 μm as described above is conveyed to thesubsequent dicing step where it is cut along the streets 21 by a dicingmachine such as a cutting machine or the like and divided intoindividual semiconductor chips.

Industrial Utilization Feasibility

[0021] In the method of processing a semiconductor wafer to apredetermined thickness according to the present invention, thestress-reducing step of reducing the stress of a coating layer byforming a plurality of grooves in the coating layer formed on the frontsurface of the semiconductor wafer is carried out before the backsurface of the semiconductor wafer is ground. Therefore, even when theback surface of the semiconductor wafer is ground thin, the occurrenceof warping is inhibited as the stress of the coating layer has beenreduced. Therefore, the dicing work that is the subsequent step can becarried out smoothly.

1. A method of processing a semiconductor wafer that has circuits in aplurality of regions sectioned by a plurality of streets on the frontsurface and has a coating layer formed on the front surface having thecircuits to a predetermined thickness, the method comprising: astress-reducing step of reducing the stress of the coating layer byforming a plurality of grooves in the coating layer formed on the frontsurface of the semiconductor wafer; and a grinding step of processingthe back surface of the semiconductor wafer by grinding to apredetermined thickness after the stress-reducing-step.
 2. The method ofprocessing a semiconductor wafer according to claim 1, wherein theplural grooves to be formed in the coating layer in the stress-reducingstep are formed along the plurality of streets.
 3. The method ofprocessing a semiconductor wafer according to claim 1, wherein theplural grooves to be formed in the coating layer in the abovestress-reducing step are formed by cutting by moving the semiconductorwafer relatively to the cutting blade while the cutting blade isrotated.